1. Field of the Invention
The present invention relates in general to network devices and, in particular, to structures for interconnecting components or sub-assemblies in the network devices.
2. Prior Art
The efficiency and effectiveness of a computer network are measured by the quantity and speed with which data is transported. A conventional computer network includes a plurality of interconnecting devices (e.g., routers, bridges, switches, etc.) coupled by communications media. In order for the network to meet a particular speed/bandwidth requirement, the routers and other interconnecting devices must be able to operate at a relatively fast rate.
One of the popular architectures used in configuring interconnecting devices is the shared bus. Examples of the shared bus architecture include Industry Standard Architecture (ISA), Peripheral Component Interconnect (PCI), etc.
In the shared bus architecture, a common bus structure is used to interconnect adapter cards to the Central Processing Unit (CPU). This type of architecture works well so long as a reasonable number of adapters are connected to the bus. However, as more adapters are added to increase connectivity, bus bandwidth and bus access latency could degenerate to become performance limiting factors.
U.S. Pat. No. 5,625,790 discloses a programmable back plan system for interconnecting printed circuit boards (PCBs). The programmable backplane consists of a motherboard with receptacles to receive the PCBs and a field programmable interconnect device (cross point switch) mounted on the motherboard. All communications are channeled through the switch. One of the shortcomings of this patent is that it provides no alternate path for communication. It is believed that some functions are better served if communication is effectuated in other ways than through a switch.
U.S. Pat. No. 5,603,044 discloses an interconnection network consisting of a pair of backplanes arranged in abutting side by side relationship. Each backplane has connector modules for receiving node cards. Selected connector modules are interconnected by permanent wiring harness on each backplane. Selected connector modules are interconnected by cables between the backplanes. Even though this patent works well for its intended purpose, it requires an unnecessary large surface area due to the side-by-side orientation of the backplanes. Most network devices, such as routers, etc., are provided relatively small spaces in wiring closets. As a consequence, the design and packaging of these devices must reflect space consideration. Therefore, the arrangement of side-by-side backplanes is probably not suitable for network devices.
U.S. Pat. No. 4,658,333 discloses a backplane with extendable capabilities to service variable groups of boards. This is accomplished by two different types of circuit boards. One type of circuit board acts as xe2x80x9cinterface/terminationxe2x80x9d for the bus. The other type acts to extend the bus to adjacent connectors. Even though the bus has extension capabilities, it is still a single bus which is subject to the overload condition set forth above.
Still, other interconnection structures are shown and described in U.S. Pat. Nos. 5,533,201; 5,122,691 and 4,831,634. The described interconnections are primarily for computer structure and not necessarily for other types of network devices.
In view of the above, there is a need for an interconnection structure that is best suited for network devices. The interconnection structure includes stacked displaced backplanes wherein one of the backplanes is provided with a primary bus structure and the other backplane is provided with a secondary bus structure. A first set of connectors are provided on one of the backplane. The first set of connectors are electrically coupled to the primary bus structure. A second set of connectors are provided on said one of the backplane. The second set of connectors are electrically coupled to the secondary bus structure on the other backplane. A third set of connectors are provided on said one of the backplane. The third set of connectors have feed through pins electrically coupled to the secondary bus structure and non-feed through pins electrically coupled to the primary bus structure.
In one feature of the invention, the connectors with feed through pins provide the mechanical structure for supporting the secondary backplane.
The connectors serve as receptacles for cards. Several preferred way of populating the respective backplanes with the cards are set forth below.